Listening in background noise is one of the most difficult listening situations, ranking as the primary complaint among hearing aid users and a common complaint among the elderly. Despite the prevalence of perception-in-noise data in these populations, it remains unclear how human cortical encoding of signals in noise contributes to perceptual abilities in these populations. A significant portion of the variability in perception-in-noise performance may be explained by neural encoding differences across individuals. Therefore, the purpose of the research proposed is to better characterize the neural encoding of speech signals in noise and relate that encoding to behavior. Cortical auditory evoked potentials together with behavioral signal-in-noise testing will be used to answer three questions. (1) What is the effect of signal-to- noise ratio (SNR) on cortical encoding of signals in noise? (2) What are the effects of background noise type on cortical encoding of signals in noise? (3) How does the cortical representation of signals in noise correlate with perception of signals in noise? To answer these questions, signal-to-noise ratio and background noise type will be varied across four groups (young normal hearing, young hearing impaired, old normal hearing, and old hearing impaired). It is hoped that the combination of physiological and behavioral information will improve our understanding of perception-in-noise variability and lead to improved diagnosis and treatment of signal-in-noise deficits.